1. Field of the Invention
The present invention relates to a liquid crystal optical modulation element and, more particularly, to a liquid crystal optical modulation element for selectively deriving a light beam within a predetermined wavelength range from white light, and a color filter and a liquid crystal display device using this element.
2. Description of the Prior Art
As field sequential display elements, various types of elements have been proposed. For example, a display element using a color filter disk is shown in Shunsuke Kobayashi “Color Liquid Crystal Display”, 1990, p. 117. According to this method, a color filter disk selectively colored in red, green, and blue, which are the three primary colors of light, is placed in front of a monochromatic CRT, and is rotated in synchronism with display operation. This enables color display. When a color filter disk is placed in front of a white light source and a black shutter (monochromatic shutter type display element) is combined with them, color display is similarly possible.
Another method is described in “Color Liquid Crystal Display” cited above, pp. 120 and 121. This method performs field sequential color display by inserting a combination of two high-speed liquid crystal display elements called π cells, a polarization plate, and three color polarization plates in front of a monochromatic CRT.
“Color Liquid Crystal Display” cited above also shows, on pp. 122 and 123, a case wherein a CRT, an LED, or a cold cathode tube is used as a backlight and a liquid lb crystal display is used as a black shutter. According to this method, backlights of three primary colors are prepared and are flashed alternately at a high speed. An example of this arrangement is shown in Gekkan Display, July 1998, pp. 11 to 16 as a field sequential full-color LCD. In this example, cold cathode tube backlights serving as illumination light sources of a currently available liquid crystal display device are switched on the time base among red, green, and blue.
In this manner, techniques that perform field sequential display in accordance with various methods have been conventionally proposed.
According to the conventional methods which respectively use, among the field sequential display elements, the color disk, and the three polarization plates and the π cells have a drawback of a low light utilization due to the presence of a light absorption layer. This is because the color disk method must use a color filter that absorbs light having a wavelength outside a specific wavelength range, and the method using the π cells requires a polarization plate using a light absorber in order to generate polarized light.
According to the conventional method which uses, among the field sequential display elements, the backlight has a drawback that it must use three types of light sources. More specifically, in additive mixture of color stimuli using three primary colors of light, three types of light are indispensable, and light sources of three different colors corresponding to the three primary colors are required. This increases the size of the device and complicates a light source driving circuit, making downsizing and cost reduction very difficult.